1. Field of the Invention
The present invention relates to a method for forming an inductor in a semiconductor device. More specifically, the present invention relates to a method for forming an inductor in a semiconductor device wherein a thickness at line and contact portions of the inductor being a passive device in RE MEMS, RFCMOS, Bipolor/SiGe and BiCMOS semiconductor devices is made uniform, whereby a high Q inductor can be manufactured.
2. Discussion of Related Art
In RE MEMS, RFCMOS, Bipolor/SiGe and BiCMOS semiconductor devices, an inductor being a passive device is formed by means of a damascene process and an inductor of a high quality is required as the level of integration is increased.
FIG. 1A to FIG. 1F are cross-sectional views shown to explain a conventional method for forming an inductor in a semiconductor device.
Referring to FIG. 1A, a lower electrode 11 is formed using a conductive material such as copper on a substrate 10 in which a predetermined underlying structure constituting a semiconductor device is formed. A positive photoresist layer 12 is covered on the substrate 10 including the lower electrode 11.
By reference to FIG. 1B, a primary exposure process is performed for a portion of the positive photoresist layer 12 up to the lower electrode 11 using a first mask 13, thus forming a first exposure region 12H in a portion where a contact of the inductor will be formed.
Referring to FIG. 1C, a secondary exposure process is performed for a portion of the positive photoresist layer 12 in a predetermined thickness using a first mask 14, thus forming second exposure regions 12T in portions where lines of the inductor will be formed.
By reference to FIG. 1D, the first and second exposure regions 12H and 12T are developed to form trenches 15 in which the lines of the inductor will be formed and a via hole 16 in which a contact of the inductor is to be formed.
Referring to FIG. 1E, the trenches 15 and the via hole 16 are buried with copper, thus forming an inductor 17.
By reference to FIG. 1F, the positive photoresist layer 12 is stripped to form the inductor 17 that is spaced apart from the substrate 10 by a predetermined distance.
Recently, there is a trend that devices for communications such as a RF inductor are integrated on a semiconductor device using MEMS technology. It is possible to fabricate a line width within several tens of μm in thickness. This principle is based on Faraday's Law and Lenz's Law and is characterized in that a conductor has a circular shape in which a plurality of coils are wound. One of methods for increasing efficiency of such a device is to reduce the dielectric constant between the conductor and a substrate or the conductor and a conductor. Public attention for a method for manufacturing a circuit with it exposed in the air on the top of a substrate has recently been attracted. In this method, the circuit is exposed in the air through twice-exposure process using a photoresist. The exposure process includes a shallows exposure process for forming the trenches 15 being an inductor line portion, as shown in FIG. 1C. In the shallow exposure process, the depth that the photoresist layer is developed is controlled through energy for illuminating light, thus controlling a thickness of the lines of the inductor that are finally formed. This method, however, has a difficulty in controlling a line thickness exactly and uniformly. This is because the amount of a photoresist that is developed is irregular because of various external environment such as composition of the photoresist, composition or components of a photoresist (PR) developer, a process condition used, image contrast of light illuminated, energy and so on. Accordingly, patterns are curved at the edge portions in view of the shallow exposure process, like a profile of the trenches 15 shown in FIG. 1D. This degrades reappearance in process. Accordingly, there are problems that reliability of the final inductor 17 is degraded and it is difficult to fabricate a high Q inductor, as shown in FIG. 1F.